VOL. LXXIV.] PHILOSOPHICAL TRANSACTIONS. Q\\ 



37-f . Probably the weather did not continue clear the whole night; if it had, 

 it is likely the degrees of cold would have been found proportionably greater at 

 every station. On the morning of the 4th there fell a misty rain, which conti- 

 nued only till noon, when the sky became clear again, and continued so till the 

 7th; during which time the nocturnal heights of the thermometers differed 

 considerably from each other; but on the sky's becoming cloudy, the local varia- 

 tion ceased. 



By experiments of this kind it may possibly in some measure be found, how 

 far evaporations from the earth, at certain times, or vapours ascending, descend- 

 ing, or meeting, in different parts of the atmosphere, may increase or diminish 

 the heat of the air in those places: or whether different degrees of heat and cold, 

 subject however to change, may not be found in different strata of air, or vapour, 

 floating in different parts of the atmosphere; or in what degree and proportion 

 the cold increases at different altitudes, and in different seasons of the year; 

 whether the cold, which is known to be very intense in the summer time on the 

 tops of high mountains, receives a proportional increase, or be not less subject 

 to variety by the return of winter and summer, night and day, than what we ex- 

 perience in the plains below. 



JiXXIII. Of some Observations tending to Investigate the Construction oj the 

 Heavens. By Wm. Herschel, Esq., F. R. S. p. 437- 



In a former paper I mentioned that a more powerful instrument was preparing 

 for continuing my reviews of the heavens. The telescope I have lately com- 

 pleted, though far inferior in size to the one I had undertaken to construct when 

 that paper was written, is of the Newtonian form, the object speculum being of 

 20 feet focal length, and its aperture 18-jV inches. The apparatus on which it 

 is mounted is contrived so as at present to confine the instrument to a meridional 

 situation, and by its motions to give the right ascension and declination of a 

 celestial object in a coarse way; which however is sufficiently accurate to point 

 out the place of the object, so that it may be found again. 



Hitherto the sidereal heavens have, not inadequately for the purpose designed, 

 been represented by the concave surface of a sphere, in the centre of which the 

 eye of an observer might be supposed to be placed. It is true the various mag- 

 nitudes of the fixed stars even then plainly suggested to us, and would have 

 better suited, the idea of an expanded firmament of 3 dimensions; but the ob- 

 servations on which I am now going to enter still further illustrate and enforce 

 the necessity of considering the heavens in this point of view. In future, there- 

 fore, we shall consider those regions into which we may now penetrate by means 

 of such large telescopes, as a naturalist regards a rich extent of ground or chain 

 of mountains, containing strata variously inclined and directed, as well as con- 



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